flex Expert System Toolkit - LPIS

7. Knowledge Specification Language 86
Rulesets
The ruleset is the construct which governs the running of the forward
chaining engine. Defining the ruleset determines which rules will be
considered for firing (i.e. the initial rule agenda), in what order they will be
considered, when the forward chaining will terminate etc.
Recall that each cycle of the forward chaining engine fires one rule, that rule
being the first rule found whose conditions are satisfied (or the rule with the
highest score out of all rules whose conditions are satisfied, if conflict
resolution is being used). The search for the rule to fire always starts at the
beginning of the list of rules in the current rule agenda. Rules may be
removed, added or re-ordered after each cycle.
A flex program is run by starting the forward-chaining engine, using the
KSL directive invoke ruleset; normally this will be as part of an
action, which can then be run from the Prolog command line as a normal
Prolog query.
Within a ruleset you can specify:
• The initial rule agenda (this is mandatory).
• The initiation directives to be performed prior to starting the engine.
• The conditions which can terminate the engine.
• The rule selection algorithm to be used.
• The rule agenda update algorithm to be used.
• The procedure to be used when a rule misfires.
Any combination of the above specifications may be included in the
definition of a ruleset. The only specification which is mandatory is the initial
rule agenda; all other specifications are optional.
The most general format of a ruleset is as follows.
ruleset Name
contains rule(s) ;
initiate by doing directive(s) ;
terminate when conditions(s) ;
select rule using rule_selection ;
update ruleset agenda_update ;
when a rule misfires do directive(s) .
Specifying The Initial Rule Agenda
The simplest declaration of a ruleset is just to state which rules are to be
used, using the KSL keyword
flex toolkit